1. Field of the Disclosure
This disclosure relates generally to catalyst materials and, more particularly, to the influence of a plurality of coating processes on performance of Zero-PGM (ZPGM) three-way catalyst (TWC) applications.
2. Background Information
The emissions present in the exhaust gas of a motor vehicle can be divided into primary and secondary emissions. Primary emission refers to pollutant gases which form directly through the combustion process of the fuel in the engine and are already present in the untreated emission before it passes through an exhaust gas treatment system. Secondary emission refers to those pollutant gases which can form as by-products in the exhaust gas treatment system.
Compliance with the emissions limits prescribed by worldwide legislation requires nitrogen oxide removal from the exhaust gas, although carbon monoxide and hydrocarbon pollutant gases from the lean exhaust gas can easily be rendered harmless by oxidation over a suitable catalyst, the reduction of the nitrogen oxides to nitrogen is much more difficult owing to the high oxygen content of the exhaust gas stream.
Catalysts attributes of activity, stability, selectivity, and regenerability in long-term service can be related to the physical and chemical properties of the catalyst materials, which in turn can be related to the method of preparation of the catalyst. The slurry characteristics of materials used are influential to the coating properties, which can be achieved by using different coating processes. A process for coating of sufficient loading may provide improved active sites for catalytic performance. As an ineffectual coating technique may result in heterogeneity of the applied coating, the preparation path for coatings may show critical factors which can influence the coating quality and catalytic performance.
Current three-way catalyst (TWC) systems include a support of alumina upon which both platinum group metals (PGM) material and promoting oxides are deposited. Key to the desired catalytic conversions is the structure-reactivity interplay between the promoting oxide and the PGM metals, in particular regarding the storage/release of oxygen under process conditions, but a set of characteristic variables drive up PGM cost, i.e., small market circulation volume, constant fluctuations in price, and constant risk to stable supply, amongst others.
According to the foregoing reasons, there may be a need to provide material compositions for PGM-free catalyst systems which may be manufactured cost-effectively, such that catalytic performance may be improved for a minimum loading, employing coating processes leading to the realization of suitable PGM-free catalytic layers in catalysts that can be used in a variety of environments and TWC applications.